1. Field of the Invention
The present invention relates to a drive control circuit used to control the drive of a linear vibration motor, including a vibrator and a stator, where the vibrator linearly oscillates back and forth relative to the stator.
2. Description of the Related Art
Though a linear vibration motor is used for a specific purpose of moving an electric shaver and the like, its use is expanding in recent years. For example, the linear vibration motor is used for an element that creates a vibration with which an operation feeling of a touch panel pressed down is to be fed back to a user. As haptics (sense of touch) engineering is finding rapidly increasing use, it is expected that the total number of linear vibration motors shipped from factories be on the increase.
The linear vibration motor is preferably driven at a frequency as close to its eigen frequency as possible (hereinafter, this eigen frequency will be referred to as “resonance frequency” also). The linear vibration motor generates the most powerful vibration when the resonance frequency thereof agrees with the drive frequency.
Since the eigen frequency of the linear vibration motor is determined by the mass of the vibrator and the spring constant, the eigen frequency varies from one product to another. Thus, in the conventional method where a fixed drive frequency is set to all drive circuits for the linear vibration motors, there are drive circuits with a significant disagreement between the eigen frequency of the motor and the drive frequency thereof, thereby causing a drop in the yield. Also, even though the eigen frequency of the motor and the drive frequency thereof agree at first, there are cases where they deviate from each other with time and the vibration gets weaker.
The present inventor has found the method such that the eigen frequency of the linear vibration motor is estimated base on a detection position of the zero cross of an induced voltage occurring in the coil of the electromagnet and the adaptive control is performed in such a manner that the eigen frequency is made to agree with the frequency of the drive signal of the linear vibration motor.